Selective Hydrogenation Process Using Layered Catalyst Composition and Preparation of Said Catalyst

ABSTRACT

A selective hydrogenation process and a layered catalyst composition for use in the selective hydrogenation process are disclosed. The process is useful for the selective hydrogenation of diolefins having from about 8 to about 19 carbon atoms per molecule to monoolefins.

CROSS REFERENCE TO RELATED APPLICATION

This application is a Division of prior copending application Ser. No.11/312,999, filed Dec. 20, 2005, now allowed, which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The invention relates to the selective hydrogenation of hydrocarbons.More specifically, the invention relates to the use and preparation of acatalyst to selectively hydrogenate C₈-C₁₉ diolefins to C₈-C₁₉monoolefins.

BACKGROUND OF THE INVENTION

The present invention relates to the use and preparation of a layeredcatalyst to selectively hydrogenate C₈-C₁₉ diolefins to C₈-C₁₉monoolefins. C₈-C₁₉ monoolefins are valuable intermediates in themanufacture of alkylbenzene detergent precursors. The layered catalystcomposition comprises an IUPAC Group 10 metal and an IUPAC Group 11metal on a layered composition support. The support comprises an innercore of a refractory inorganic component, such as cordierite and anouter layer of a refractory inorganic component, such as gamma alumina.

Most detergents that are on the worldwide market today are made oflinear alkylbenzene sulfonates (LABS). The linear alkylbenzenessulfonates are preferred because they biodegrade more rapidly than thebranched variety. LABS are manufactured from linear alkyl benzenes(LAB). The petrochemical industry produces LAB by catalyticallydehydrogenating linear paraffins to linear olefins and then alkylatingbenzene with the linear olefins in the presence of a catalyst. Thislinear paraffin dehydrogenation step produces as its major productlinear monoolefins. However, it is also well known that the catalyticdehydrogenation step of linear paraffins also produces an amount oflinear diolefins. These diolefins do not alkylate benzene in the sameway as the monoolefins and therefore do not produce the desireddetergent precursors. Selective diolefin hydrogenation converts thediolefins to monoolefins, which can then be used to produce LAB. Adetailed outline of LAB processes is provided in U.S. Pat. No.5,276,231, the contents of which are herein incorporated in itsentirety.

The current industrial practice for selectively hydrogenating diolefinsor unsaturated hydrocarbon fractions is based on the use of sulfidednickel catalysts operating at moderately high temperatures ofapproximately 185° C. (365° F.). Sulfur loss from the catalyst to theproduct occurs and sulfur must be replenished to keep the catalystactive and operating optimally. Furthermore, once the sulfur is lostinto the product, in some instances the sulfur must also be removed fromthe product and this adds another level of processing. U.S. Pat. No.4,992,157 describes a selective hydrogenation catalyst comprisingsulfided nickel and an IUPAC Group 10 metal on an alumina/clay support.

Other types of selective hydrogenation processes are also known, such asthat described in JP54157507A. JP 54157507A describes the use of apalladium catalyst on an alumina support to selectively hydrogenateacetylene and methyl acetylene (alkynes) that are present in olefinfractions obtained in petrochemical processes. The catalyst described inJP54157507A comprises a thin alumina coating over an alpha aluminacarrier of spherical or cylindrical shape and being around 1-20 mm insize, length and diameter. The alumina precursor, which can be aluminumnitrate, aluminum chloride, aluminum hydroxide and the like, is coatedonto the alpha alumina carrier and then the coated alpha alumina carrierand alumina precursor is heat treated at between 400° C. (752° F.) to700° C. (1292° F.) to create a thin alumina coating over the alphaalumina carrier. A palladium compound such as palladium chloride,palladium nitrate, and the like is dissolved in a suitable solvent, andthen applied to the alumina coating to give effectively an enrichedsurface coating containing palladium. JP54157507A describes the use ofthe resulting catalyst in the selective hydrogenation of acetylene in acomposition comprising ethylene.

The process disclosed herein has been developed to enable one toselectively hydrogenate C₈-C₁₉ diolefins to C₈-C₁₉ monoolefins atrelatively high space velocities using a layered catalyst thateliminates the need to use a sulfided nickel catalyst for associatedsulfur addition (and in some instances the subsequent removal of sulfurfrom the product).

INFORMATION DISCLOSURE

US 2003/0036476 A1 describes a coated catalyst having a core and a shellsurrounding the core, the core is made up of an inert support material.The shell is made up of a porous support substance, and the shell isphysically attached to the core. A catalytically active metal selectedfrom the group consisting of the metals of the 10th and 11th groups ofthe Periodic Table of the Elements is present in finely divided form inthe shell. The coated catalyst is described as being suitable for theselective reduction of unsaturated hydrocarbons, specifically lowerC₂-C₄ unsaturated hydrocarbons.

U.S. Pat. No. 6,177,381 B1, which is incorporated by reference in itsentirety, describes a layered catalyst composition showing improveddurability and selectivity for dehydrogenating hydrocarbons, a processfor preparing the catalyst and processes for using the composition. Thecatalyst composition comprises an inner core such as alpha-alumina, andan outer layer bonded to the inner core composed of an outer refractoryinorganic oxide such as gamma-alumina. The outer layer has uniformlydispersed thereon a platinum group metal such as platinum and a promotermetal such as tin. The composition also contains a modifier metal suchas lithium. The catalyst composition is prepared by using an organicbinding agent such as polyvinyl alcohol which increases the bond betweenthe outer layer and the inner core. The catalyst composition isdescribed as also being suitable for hydrogenation.

BRIEF SUMMARY OF THE INVENTION

The process disclosed herein uses a layered catalyst for the treatmentof a hydrocarbon stream containing a mixture of at least C₈-C₁₉diolefins and C₈-C₁₉ monoolefins. The process and catalyst are employedto selectively hydrogenate C₈-C₁₉ diolefins to C₈-C₁₉ monoolefins atrelatively high space velocities and without hydrogenating substantiallythe C₈-C₁₉ monoolefins originally present in the mixture. A process forpreparing the layered catalyst is also provided herein.

In accordance with one embodiment of the present invention there isprovided a process for selectively hydrogenating a C₈-C₁₉ diolefin to aC₈-C₁₉ monoolefin in a hydrocarbon mixture comprising the C₈-C₁₉diolefin and the C₈-C₁₉ monoolefin, the process comprising the steps of:

(i) bringing the hydrocarbon mixture under selective hydrogenationconditions into contact with a catalyst to give substantially a C₈-C₁₉monoolefin product; wherein the catalyst comprises

-   -   (a) an inner core comprising a first refractory inorganic        component,    -   (b) an outer layer bonded to said inner core, said outer layer        comprising a second refractory inorganic component having        dispersed thereon at least one IUPAC Group 10 metal and at least        one IUPAC Group 11 metal.        In one aspect of the embodiment defined above, the process can        be further characterized in that the catalyst is prepared by a        method comprising depositing the at least one IUPAC Group 10        metal and the at least one IUPAC Group 11 metal on the second        refractory inorganic component after the outer layer is bonded        to the inner core. In another aspect of the embodiment the        process can also be further characterized in that the outer        layer is in the presence of a liquid phase during the deposition        of the at least one IUPAC Group 10 metal and the at least one        IUPAC Group 11 metal onto the second refractory inorganic        component.

In accordance with another embodiment of the present invention there isprovided a process for preparing a layered catalyst composition forselectively hydrogenating a C₈-C₁₉ diolefin to a C₈-C₁₉ monoolefin in ahydrocarbon mixture comprising the C₈-C₁₉ diolefin and the C₈-C₁₉monoolefin at selective hydrogenation conditions comprising a firstliquid phase, wherein the catalyst comprises:

-   -   a. an inner core comprising a first refractory inorganic        component,    -   b. an outer layer bonded to said inner core, the outer layer        comprising a second refractory inorganic component having        dispersed thereon at least one IUPAC Group 10 metal and at least        one IUPAC Group 11 metal, the process comprising:    -   i) coating an inner core with a slurry comprising the second        refractory inorganic component, depositing on the coated core at        least one IUPAC Group 10 metal and at least one IUPAC Group 11        metal in the presence of a second liquid phase, drying the        coated core and calcining at a temperature of about 400 to about        900° C. (752 to 1652° F.) for a time sufficient to bond the        outer layer to the inner core and provide a layered support; and    -   ii) reducing the product of step i) under reduction conditions        to provide the layered catalyst composition.        In one aspect this embodiment can be further characterized in        that the at least one IUPAC Group 10 metal and the at least one        IUPAC Group 11 metal are dispersed on the second refractory        inorganic component by an impregnation step.

The selective hydrogenation process disclosed herein is believed to becapable of operating at relatively higher space velocities for a givenreaction temperature and equilibrium conversion of diunsaturates thanprior processes. Without limiting this invention to any particulartheory, it is believed the layered catalyst used in the selectivehydrogenation process disclosed herein has less restrictions todiffusion of reactants and products in comparison to previous catalysts.Consequently, it is expected that the temperature required to attain aspecified equilibrium conversion would be lower and also that at a givenconversion higher space velocities could be attained without excessivereactor temperature. Therefore, less catalyst and a smaller reactorwould be needed, which would result in reduction in the capital cost ofthe process.

BRIEF DESCRIPTION OF THE DRAWING

The attached drawing shows the adsorption and desorption profiles forcatalysts of Examples 3 and 4 plotted against the pore radius and thedifferential volume of the catalysts.

The embodiments and objects of the invention will become clearer afterthe following detailed description.

DETAILED DESCRIPTION OF THE INVENTION

As stated, a selective hydrogenation process and a layered catalystcomposition for use in the selective hydrogenation process are disclosedherein.

Specifically, the process disclosed herein relates to the selectivehydrogenation of C₈-C₁₉ diolefins in a mixture of C₈-C₁₉ monolefins. TheC₈-C₁₉ diolefins are selectively hydrogenated to the correspondingC₈-C₁₉ monoolefins with little or no hydrogenation of the originalC₈-C₁₉ monoolefins. The desired C₈-C₁₉ monoolefin product is typicallyin the kerosene boiling range and is an intermediate in the manufactureof alkylbenzene detergent precursors. The selective hydrogenation occurswhen the hydrocarbon mixture comprising C₈-C₁₉ diolefins and C₈-C₁₉monolefins is brought into contact with a layered catalyst of theinvention under selective hydrogenation conditions. Preferred selectivehydrogenation conditions for example, without limitation includepressures of about 0 kPa(g) (0 psi(g)) to about 13,789 kPa(g) (2000psi(g)), temperatures of between 30° C. (86° F.) and 180° C. (356° F.),H₂ to diolefin mole ratios of about 1:1 to about 2:1, preferably about1.1:1 to about 1.5:1 and liquid hourly space velocities (LHSV) of about0.1 to about 20 hr⁻¹.

The layered catalyst composition comprises an inner core composed of arefractory inorganic component, which has substantially lower adsorptivecapacity for catalytic metal precursors relative to the outer layer.Examples of refractory inorganic components suitable for the inner coreinclude without limitation alpha alumina, theta alumina, siliconcarbide, metals, cordierite, zirconia, titania and mixtures thereof. Apreferred inorganic component for the inner core is cordierite.

The inner core can be formed into a variety of shapes such as pellets,extrudates, spheres or irregularly shaped particles. It is recognized,however, that not all materials can be formed into any shape.Preparation of the inner core can be done by means known in the art suchas oil dropping, pressure molding, metal forming, pelletizing,granulation, extrusion, rolling methods and marumerizing. A spherical orcylindrical inner core is preferred. Once the inner core is prepared, itis calcined at a temperature of about 400° C. (752° C.) to about 1500°C. (2732° F.).

The inner core is then coated with an outer layer of a refractoryinorganic component which is the same or different from the inorganiccomponent which may be used as the inner core. Examples of refractoryinorganic components suitable for the outer layer include withoutlimitation alpha alumina, theta alumina, silicon carbide, metals,cordierite, zirconia, titania, gamma alumina, delta alumina, etaalumina, silica/alumina, zeolites, non-zeolitic molecular sieves (NZMS),and mixtures thereof. This outer layer of refractory component is onewhich has a relatively high surface area of between about 50 and 200m²/g based on the weight of the outer layer. The outer layer thicknessis between about 50 and 300 micron, preferably between about 50 and 100micron. The outer layer has a number of pores distributed across itssurface. The pores in the outer layer of the catalyst will preferablyhave an average pore radius of between 65 to 75 Angstrom. The poreradius size distribution will however, vary from approximately 20 to 250Angstrom. The pore volume is substantially proportional to the thicknessof the outer layer and the average radius of the pores. Where the outerlayer is approximately 100 micron thick, the total pore volume will beapproximately 0.10 to 0.15 cc/g. Where the outer layer is approximately200 micron thick, the total pore volume will be approximately 0.20 to0.30 cc/g. The surface area of a catalyst having a 100 micron thickouter layer will be approximately 35 m²/g, while the surface area of acatalyst having a 200 micron thick outer layer will be approximately 65m²/g, based on the weight of the catalyst.

It should be pointed out that silica/alumina is not a physical mixtureof silica and alumina but means an acidic and amorphous material thathas been cogelled or coprecipitated. This term is well known in the art,see e.g., U.S. Pat. Nos. 3,909,450; 3,274,124; and 4,988,659, all ofwhich are incorporated by reference in their entireties. Examples ofzeolites include, but are not limited to, zeolite Y, zeolite X, zeoliteL, zeolite beta, ferrierite, MFI, mordenite and erionite. Non-zeoliticmolecular sieves (NZMS) are those molecular sieves which containelements other than aluminum and silicon and includesilicoaluminophosphates (SAPOs) described in U.S. Pat. No. 4,440,871,ELAPOs described in U.S. Pat. No. 4,793,984, MeAPOs described in U.S.Pat. No. 4,567,029 all of which are incorporated by reference in theirentireties. A preferred inorganic component for the outer layer is gammaalumina.

A preferred way of preparing a gamma alumina is by the well-known oildrop method which is described in U.S. Pat. No. 2,620,314, which isincorporated by reference in its entirety. The oil drop method comprisesforming an aluminum hydrosol by any of the techniques taught in the artand preferably by reacting aluminum metal with hydrochloric acid;combining the hydrosol with a suitable gelling agent, e.g.,hexamethylenetetraamine; and dropping the resultant mixture into an oilbath maintained at elevated temperatures (about 93° C. (199° F.)). Thedroplets of the mixture remain in the oil bath until they set and formhydrogel spheres. The spheres are then continuously withdrawn from theoil bath and typically subjected to specific aging and drying treatmentsin oil and ammoniacal solutions to further improve their physicalcharacteristics. The resulting aged and gelled spheres are then washedand dried at a relatively low temperature of about 80° C. (176° F.) to260° C. (500° F.) and then calcined at a temperature of about 455° C.(851° F.) to 705° C. (1301° F.) for a period of about 1 to about 20 hr.This treatment effects conversion of the hydrogel to the correspondingcrystalline gamma alumina.

The layer is applied by forming a slurry of the outer refractorycomponent and then coating the inner core with the slurry by means wellknown in the art. Slurries of inorganic components can be prepared bymeans well known in the art which usually involve the use of a peptizingagent. For example, any of the transitional aluminas can be mixed withwater and an acid such as nitric, hydrochloric, or sulfuric to give aslurry. Alternatively, an aluminum sol can be made by for example,dissolving aluminum metal in hydrochloric acid and then mixing thealuminum sol with the alumina powder.

The slurry can also contain an organic bonding agent which aids in theadhesion of the layer material to the inner core. Examples of thisorganic bonding agent include but are not limited to polyvinyl alcohol(PVA), hydroxy propyl cellulose, methyl cellulose and carboxy methylcellulose. The amount of organic bonding agent which is added to theslurry will vary considerably from about 0.1 wt-% to about 3 wt-% of theslurry. How strongly the outer layer is bonded to the inner core can bemeasured by the amount of layer material lost during an attrition test,i.e., attrition loss. Loss of the second refractory component byattrition is measured by agitating the catalyst, collecting the finesand calculating an attrition loss, in the manner described in Example 11in U.S. Pat. No. 6,177,381 B1. It has been found that by using anorganic bonding agent as described above, the attrition loss is lessthan about 10 wt-% of the outer layer.

Depending on the particle size of the outer refractory inorganiccomponent, it may be necessary to mill the slurry in order to reduce theparticle size and simultaneously give a narrower particle sizedistribution. This can be done by means known in the art such as ballmilling for times of about 30 min to about 5 hr and preferably fromabout 1.5 to about 3 hr. It has been found that using a slurry with anarrow particle size distribution improves the bonding of the outerlayer to the inner core. Without wishing to be bound by any particulartheory, it appears that bonding agents such as PVA aid in making aninterlocking bond between the outer layer material and the inner core.Whether this occurs by the PVA reducing the surface tension of the coreor by some other mechanism is not clear. What is clear is that aconsiderable reduction in loss of the outer layer by attrition isobserved.

The slurry may also contain an inorganic bonding agent selected from analumina bonding agent, a silica bonding agent or mixtures thereof.Examples of silica bonding agents include silica sol and silica gel,while examples of alumina bonding agents include alumina sol, boehmiteand aluminum nitrate. The inorganic bonding agents are converted toalumina or silica in the finished composition. The amount of inorganicbonding agent varies from about 2 to about 15 wt-% as the component, andbased on the weight of the slurry.

The slurry can also contain a modifier metal selected from the groupconsisting of alkali metals, alkaline earth metals and mixtures thereof.The alkali and alkaline earth metals which can be used as modifiermetals in the practice of this invention include lithium, sodium,potassium, cesium, rubidium, beryllium, magnesium, calcium, strontiumand barium. Preferred modifier metals are lithium, potassium, sodium andcesium with lithium and sodium being especially preferred. One methodinvolves preparing the slurry with a solution (preferably aqueous) of adecomposable compound of the modifier metal or modifier metal precursor.By decomposable is meant that upon heating the metal compound isconverted to the metal or metal oxide with the release of byproducts.Illustrative of the decomposable compounds of the alkali and alkalineearth metals are the halide, nitrate, carbonate or hydroxide compounds,e.g., potassium hydroxide, lithium nitrate.

Coating of the inner core with the slurry can be accomplished by meanssuch as rolling, dipping, spraying, etc. One preferred techniqueinvolves using a fixed fluidized bed of inner core particles andspraying the slurry into the bed to coat the particles evenly. Thethickness of the layer can vary considerably, but usually is from about50 to about 300 micron preferably from about 50 to about 100 micron. Itshould be pointed out that the optimum layer thickness depends on theuse for the catalyst and the choice of the outer refractory component.Once the inner core is coated with the layer of outer refractoryinorganic component, the resultant layered support is dried at atemperature of about 100° C. (212° F.) to about 320° C. (608° F.) for atime of about 1 to about 24 hr and then calcined at a temperature ofabout 400° C. (752° F.) to about 900° C. (1652° F.) for a time of about0.5 to about 10 hr to effectively bond the outer layer to the inner coreand provide a layered catalyst support. Of course, the drying andcalcining steps can be combined into one step.

Having obtained the layered catalyst support, the catalytic metalsand/or metal precursors can be dispersed on the layered support by meansknown in the art. Thus, an IUPAC Group 10 and IUPAC Group 11 metal/metalprecursor can be dispersed on the outer layer. The IUPAC Group 10 metaland/or metal precursor includes platinum and palladium. The IUPAC Group11 metal and/or metal precursor includes copper, silver and gold.

The catalytic metals can be deposited on the layered support in anysuitable manner known in the art. One method involves impregnating thelayered support with a solution (preferably aqueous) of a decomposablecompound of the metals or metal precursors. Illustrative of thedecomposable compounds of the IUPAC Group 10 metals are chloroplatinicacid, ammonium chloroplatinate, bromoplatinic acid, dinitrodiaminoplatinum, sodium tetranitroplatinate, palladium chloride, palladiumnitrate, diamminepalladium hydroxide, tetraamminepalladium chloride, andorganometallic compounds such as palladium bis π-allyl and palladiumbis-acetylacetonate. Illustrative of the decomposable compounds of theIUPAC Group 11 metals are copper nitrate, copper acetylacetonate, copperacetate, copper bromide, copper butanoate, copper chloride, copperchlorate, copper citrate, copper formate, copper perchlorate, coppertartrate, silver nitrate, silver acetate, silver carbonate, silverchlorate, silver nitrite, silver perchlorate, and gold bromide.

The catalyst also preferably contains an alkali or alkaline earth metalfrom IUPAC Groups 1 or 2, examples of which include without limitationlithium, sodium, potassium, cesium, rubidium, beryllium, magnesium,calcium, strontium and barium, preferably sodium or potassium.

All of the metals can be impregnated into the outer layer using onecommon solution or they can be sequentially impregnated in any order,but not necessarily with equivalent results. A preferred impregnationprocedure involves the use of a steam-jacketed rotary dryer. Thecatalyst support is immersed in the impregnating solution containing thedesired metal compound contained in the dryer and the support is tumbledtherein by the rotating motion of the dryer. The catalyst support is inthe presence of a liquid phase, and preferably in an all-liquid phase.The impregnating solution is present in an excess relative to the amountof catalyst support so that free liquid is present. Precipitation of themetals is prevented by proper control of the pH of the impregnatingsolution. Evaporation of the solution in contact with the tumblingsupport is expedited by applying steam to the dryer jacket. Theresultant composite is allowed to dry under ambient temperatureconditions, or dried at a temperature of about 80° C. (176° F.) to about110° C. (230° F.), followed by calcination at a temperature of about400° C. (752° F.) to about 700° C. (1292° F.) for a time of about 1 toabout 4 hr, thereby converting the metal compound to the metal or metaloxide.

In one method of preparation the method involves adding one or more ofthe metal components to the outer refractory component prior to applyingit as a layer onto the inner core. For example, either the IUPAC Group10 or Group 11 metal or both can be added to the slurry. Thus, in onemethod, the catalytic metals are deposited onto the outer refractorycomponent prior to depositing the second refractory component as a layeronto the inner core. The catalytic metals can be deposited onto theouter refractory component powder in any order although not necessarilywith equivalent results.

As a final step in the preparation of the layered catalyst composition,the catalyst composition is reduced under hydrogen or other reducingatmosphere in order to ensure that the IUPAC Group 10 and 11 metalcomponents are in the metallic state (zero valent). Reduction is carriedout at a temperature of about 100° C. (212° F.) to about 650° C. (1202°F.) for a time of about 0.5 to about 10 hr in a reducing environment,preferably dry hydrogen.

In the preferred embodiments the metals are uniformly distributedthroughout the outer layer of outer refractory component and aresubstantially present only in the outer layer. It is also preferred thatthe IUPAC Group 10 and 11 metals be distributed uniformly through theouter layer. Preferably the ratio of the IUPAC Group 10 to the IUPACGroup 111 metal over the outer layer of the refractory component issubstantially constant.

The shape and size of the catalyst particles depends on a number oftechnical and economic factors and considerations, such as the allowablepressure drop across the selective hydrogenation reactor, the amount ofcatalyst and the cost of production. The preferred shape of the particleis spherical. It is preferred that the catalyst particle has a diameterof about 0.8 mm ( 1/32 in.) to 6.4 mm (¼ in.), preferably about 1.6 mmor 1600 micron ( 1/16 in.).

The hydrogenatable hydrocarbon mixtures used in the selectivehydrogenation process disclosed herein contain a diunsaturate,preferably a diolefin, and a monounsaturate, preferably a monoolefin.The unsaturates are preferably aliphatic olefins having from about 8 toabout 19, often 9 to 16, carbon atoms per molecule. In the monoolefinthe positioning of the olefinic bond is not critical to the selectivehydrogenation process disclosed herein. Conjugated diolefins, however,are more readily selectively hydrogenated to monoolefins than arenonconjugated diolefins. The position of the olefinic bond in themonoolefin is not critical when the monoolefin is used in themanufacture of alkylbenzene detergent precursors as most alkylationcatalysts have been found to promote migration of the olefinic bond. Thebranching of the hydrocarbon backbones of the monoolefin and thediolefin are not critical to the selective hydrogenation processdisclosed herein. However, the branching of the hydrocarbon backbone ofthe monoolefin is often more of a concern as the structuralconfiguration of the alkyl group on the alkylbenzene product can affectperformance. For instance, where alkylbenzenes are sulfonated to producesurfactants, undue branching can adversely affect the biodegradabilityof the surfactant. On the other hand, some branching may be desired suchas the lightly branched modified alkylbenzenes described in U.S. Pat.No. 6,187,981 B1. The olefin, be it the monoolefin or the diolefin, maybe unbranched or lightly branched, which as used herein, refers to anolefin having three or four primary carbon atoms and for which none ofthe remaining carbon atoms are quaternary carbon atoms. A primary carbonatom is a carbon atom which, although perhaps bonded also to other atomsbesides carbon, is bonded to only one carbon atom. A quaternary carbonatom is a carbon atom that is bonded to four other carbon atoms.

The aliphatic monoolefin is usually a mixture of two or moremonoolefins, and the aliphatic diolefin is usually a mixture of two ormore diolefins. For commercial processes, other components may bepresent with the olefin-containing aliphatic compounds. For instance,the monoolefin and the diolefin may be obtained by the dehydrogenationof a paraffinic feedstock and undehydrogenated paraffin, which isdifficult to separate from the olefins, is passed to the selectivehydrogenation reactor. The unreacted paraffin may be one or more normalor branched paraffins having from about 8 to 19, often 9 to 16, carbonatoms per molecule. See, for instance, U.S. Pat. No. 6,670,516 B1,herein incorporated by reference. Generally, where olefin is obtained bythe dehydrogenation of a paraffinic feedstock, the molar ratio of olefinto paraffin is between about 1:12 to 1:8; however, such amounts ofparaffin are not critical to the processes of this invention. Indeed,olefin-containing feedstocks having an essential absence of paraffinsare suitable.

The concentrations of monoolefins and diolefins in the hydrogenatablehydrocarbon mixtures are not critical to the selective hydrogenationprocess disclosed herein. The mixture can contain from about 0.5 toabout 95 mol-% monoolefins and from about 0.1 to about 20 mol-%diolefins. A suitable mixture produced by the dehydrogenation of aparaffinic feedstock usually contains from about 10 to about 15 mol-%monoolefins and from about 0.5 to about 1.5 mol-% diolefins. The molarratio of monoolefins to diolefin in the mixture is typically from about50:1 to about 5:1, preferably about 25:1 to about 7:1.

The source of the paraffinic feedstock for dehydrogenation is notcritical although certain sources of paraffinic feedstocks will likelyresult in certain impurities being present. Conventionally, kerosenefractions produced in petroleum refineries either by crude oilfractionation or by conversion processes therefor form suitable feedmixture precursors. Fractions recovered from crude oil by fractionationwill typically require hydrotreating for removal of sulfur and/ornitrogen prior to being fed to the subject process. The boiling pointrange of the kerosene fraction can be adjusted by prefractionation toadjust the carbon number range of the paraffins. In an extreme case theboiling point range can be limited such that only paraffins of a singlecarbon number predominate. Kerosene fractions contain a very largenumber of different hydrocarbons and the feed mixture to the subjectprocess can therefore contain 200 or more different compounds.

The paraffinic feedstock may alternatively be at least in part derivedfrom oligomerization or alkylation reactions. Such paraffinic feedstockmixture preparation methods are inherently imprecise and produce amixture of compounds. The paraffinic feedstock mixtures to thedehydrogenation process may contain quantities of paraffins havingmultiple branches and paraffins having multiple carbon atoms in thebranches, cycloparaffins, branched cycloparaffins, or other compoundshaving boiling points relatively close to the desired compound isomer.Thus, the paraffinic feedstock mixtures to the dehydrogenation step canalso contain sizable quantities of aromatic hydrocarbons.

Another source of paraffins is in condensate from gas wells. Usuallyinsufficient quantities of such condensate are available to be theexclusive source of paraffinic feedstock. However, its use to supplementother paraffinic feedstocks can be desirable. Typically thesecondensates contain sulfur compounds, which have restricted their use inthe past. As the selective hydrogenation process disclosed hereinenables the use of sulfur-containing feeds, these condensates can beused to supply paraffins for alkylation. Paraffins may also be producedfrom synthesis gas (Syngas), hydrogen and carbon monoxide. This processis generally referred to as the Fischer-Tropsch process. Syngas may bemade from various raw materials including natural gas and coal, thusmaking it an attractive source of paraffinic feedstock where petroleumdistillates are not available.

In some instances it may be desired to locate an alkylbenzene facilityat a location where a kerosene fraction is not readily available, orother commercial uses for a kerosene fraction render it lesseconomically attractive as a feedstock for making alkylbenzenes. Inthese instances the ability to use alternative feedstocks is highlydesirable. Alternative feedstocks include other petroleum fractions,especially naphtha range fractions, and synthesized hydrocarbons such asFischer-Tropsch materials. These raw materials have a lower molecularweight than the sought olefins for alkylation and accordingly must besubjected to a dimerization or a metathesis to generate olefins ofsuitable chain length (detergent range olefins). Numerous processes havebeen disclosed for preparing detergent olefins from these alternativefeedstocks. See, for instance, WO 2004/072005A1, WO 2004/072006A1, U.S.Patent Application Publications 2004/0030209A1, 2004/0176655A1, and2004/0199035A1. In one arrangement, the hydrogenatable hydrocarbonmixture can be produced by dehydrogenating a feed containing C₅ and C₆paraffins to produce C₅ and C₆ olefins and then reacting the C₅ and C₆olefins under chain growth conditions to provide a detergent rangeolefin product comprising C₁₀ to C₁₂ mono-olefins. The chain growthreaction step can be dimerization or metathesis which may be incombination with oligomerization.

The hydrogenatable hydrocarbon mixture to the selective hydrogenationprocess disclosed herein should be sufficiently free of impurities, suchas water, nitrogen compounds and sulfur compounds, that can undulyadversely affect the life of the selective hydrogenation catalyst. Thehydrogenatable hydrocarbon mixture may also contain aromatic byproductsproduced by dehydrogenation of the paraffinic feedstock, as described inU.S. Pat. No. 5,276,231. Alternatively, the selective aromatics removalprocess described in U.S. Pat. No. 5,276,231 may be used to remove someor essentially all of the aromatic byproducts upstream of the selectivehydrogenation process disclosed herein.

In the selective hydrogenation process disclosed herein, hydrogenatablehydrocarbon mixtures of C₈-C₁₉ diolefins and C₈-C₁₉ monoolefins arecontacted with the catalyst disclosed herein in a selectivehydrogenation zone maintained under selective hydrogenation conditions.This contacting can be accomplished in a fixed catalyst bed system, amoving catalyst bed system, a fluidized bed system, etc., or in abatch-type operation. A fixed bed system is preferred. In this fixed bedsystem the hydrocarbon feed stream is preheated to the desired reactiontemperature and then flowed into the selective hydrogenation zonecontaining a fixed bed of the catalyst. The selective hydrogenation zonemay itself comprise one or more separate reaction zones with temperatureregulation means there between to ensure that the desired reactiontemperature can be maintained at the entrance to each reaction zone. Thehydrocarbon may be contacted with the catalyst bed in either upward,downward or radial flow fashion. Downflow of the hydrocarbon through afixed catalyst bed is preferred. The catalyst may be in the presence ofa liquid phase, and preferably in either an all-liquid phase or atsupercritical conditions.

The conditions for carrying out selective hydrogenation processes arewell known in the art and can be carried out in a batch type or acontinuous type operation. Generally, selective hydrogenation conditionsinclude pressures of about 0 kPa(g) (0 psi(g)) to about 13,789 kPa(g)(2000 psi(g)), temperatures of about 30° C. (86° F.) to about 180° C.(356° F.), H₂ to diunsaturate mole ratios of about 5:1 to about 0.1:1and a liquid hourly space velocity (LHSV) of about 0.1 to about 20 hr⁻¹.It is recognized that achieving conditions where the lower H₂ todiunsaturate mole ratios is less than about 1:1 would only be desirableif the conversion needed to be limited. As used herein, diunsaturateincludes both diolefinic compounds and compounds having a triple bond.As used herein, the abbreviation “LHSV” means liquid hourly spacevelocity, which is defined as the volumetric flow rate of liquid perhour divided by the catalyst volume, where the liquid volume and thecatalyst volume are in the same volumetric units.

The effluent stream from the selective hydrogenation zone generally willcontain unconverted hydrogenatable hydrocarbons, hydrogen and theproducts of hydrogenation reactions. This effluent stream may be cooledand passed to a hydrogen separation zone to separate a hydrogen-richvapor phase from a hydrocarbon-rich liquid phase. A separate hydrogenseparation zone may not be needed where the H₂ to diunsaturate moleratio is near to 1:1. The hydrocarbon-rich liquid phase, or the effluentstream in the absence of a separate hydrogen separation zone, isseparated by means of either a suitable selective adsorbent, a selectivesolvent, a selective reaction or reactions or by means of a suitablefractionation scheme. Unconverted hydrogenatable hydrocarbons arerecovered and may be recycled to the selective hydrogenation zone. TheC₈-C₁₉ monoolefin products of the hydrogenation reactions are recoveredas final products or as intermediate products in the preparation ofother compounds.

The hydrogenatable hydrocarbons usually do not need to be admixed with adiluent material before, while or after being flowed to the selectivehydrogenation zone. The selective hydrogenation reactions of thediunsaturates to monounsaturates are considered to be only slightlyexothermic, and the temperature rise in the selective hydrogenationreactor is typically not excessive. The selective hydrogenation reactorpreferably does not have indirect heat exchange means to remove the heatas it is produced and the reactor may be adiabatic. If used, the diluentmaterial may be hydrogen or a paraffin having from 8 to 19 carbon atomsper molecule. Any diluent passed to the selective hydrogenation zonewill typically be separated from the effluent and recycled to theselective hydrogenation reaction zone.

The following examples are presented in illustration of this inventionand are not intended as undue limitations on the generally broad scopeof the invention as set out in the appended claims.

EXAMPLES Example 1

One catalyst of the invention was prepared by impregnating a cordieritesphere having a 100 micron outer layer of alumina with a liquid solutionof palladium nitrate, copper nitrate and potassium nitrate. Theresulting solution was evaporated to dryness and the sample was calcinedat 450° C. (842° F.). The sample was then reduced at 200° C. (392° F.)with hydrogen. Standard impregnation conditions and techniques wereemployed and the following metal loadings based on the weight of thecatalyst were achieved: 0.02 wt-% Pd, 0.038 wt-% Cu and 0.33 wt-% K.

Example 2

A second catalyst of the invention was prepared by impregnating acordierite sphere having a 100 micron outer layer of alumina with aliquid solution of palladium nitrate, silver nitrate and potassiumnitrate. The resulting solution was evaporated to dryness and the samplewas calcined at 450° C. (842° F.). The sample was then reduced at 200°C. (392° F.) with hydrogen. Standard impregnation conditions andtechniques were employed and the following metal loadings based on theweight of the catalyst were achieved: 0.02 wt-% Pd, 0.065 wt-% Ag, and0.33 wt-% K.

The diolefin conversion and selectivity of the catalysts prepared inExamples 1 and 2 were studied using as feed the product of a commercialcatalytic dehydrogenation unit. Based on analyses of other similar feedsfrom the same source, the feed used in Examples 1 and 2 is believed tohave the composition shown in Table 1. A volume of the catalyst to betested was loaded in a reactor, and the feed flow was started underselective hydrogenation conditions. Throughout the test, the pressurewas maintained at approximately 3447 kPa(g) (500 psi(g)), the LHSV wasapproximately 5 hr⁻¹, and a liquid phase was present. The catalyst wasevaluated over a range of 35° C. (95° F.) to 85° C. (185° F.). The molarratio of hydrogen to diolefin was 1.4. The results obtained at 55° C.(131° F.) for the catalysts prepared in Examples 1 and 2 are shown inTable 2.

Comparative Example 1

A first reference catalyst comprising 0.1% palladium on a sphericalalumina support was evaluated. A volume of this reference catalyst wastested in the manner described in Example 2. The results obtained areshown in Table 2.

Comparative Example 2

A second reference catalyst containing sulfided nickel dispersed on analumina support was evaluated. A volume of this second referencecatalyst was tested in the manner described in Example 2, except thatthe catalyst was evaluated at a temperature of 185° C. (365° F.) and themolar ratio of hydrogen to diolefin was 1.5. The results obtained areshown in Table 2.

Comparative Example 3

A third reference catalyst containing sulfided nickel dispersed on analumina support was evaluated. This reference catalyst contained lessnickel than the second reference catalyst. A volume of this thirdreference catalyst was tested in the manner described in ComparativeExample 2. The results obtained are shown in Table 2.

TABLE 1 Component Concentration, wt-% C8-minus hydrocarbons 0.31 C9paraffins 0.14 C10 paraffins 14.79-14.90 C10 monoolefins 1.73 C11paraffins 27.89-27.97 C11 monoolefins 3.80 C12 paraffins 24.36-24.43 C12monoolefins 3.9 C13 paraffins 14.65-14.69 C13 monoolefins 2.40 C14paraffins 1.14 C14 monoolefins 0.20 Total diolefins* 0.74 Unknowns3.78-3.84 *C2-C7 diolefins are negligible contributors to the totaldiolefin measurement

TABLE 2 Diolefin Temperature, Conversion, Selectivity, Catalyst ° C. (°F.) % %¹ Example 1 -- 0.02% 55 (131) 74.3 91.7 Pd/0.038% Cu Example 2 --0.02% 55 (131) 63.5 78.3 Pd/0.065% Ag Comparative Example 55 (131) 54.180 1 -- 0.1% Pd Comparative Example 185 (365) 50 52.6 2 -- sulfidednickel Comparative Example 185 (365) 66.2 70 3 -- sulfided nickel ¹Thepercentage selectivity is the percentage of diolefin hydrogenated tomonoolefin relative to the percentage of monoolefin hydrogenated toparaffin.

The results shown in Table 2 illustrate that the catalysts prepared inExamples 1 and 2 showed diolefin conversion and selectivity resultsequivalent or better than the second and third reference catalysts,while operating at approximately 130° C. (234° F.) lower in temperature.While operating at the same temperature of 55° C. (131° F.), thecatalysts prepared in Examples 1 and 2 showed better diolefin conversionthan the first reference catalyst, and the catalyst prepared in Example1 also showed better selectivity than the first reference catalyst.

Example 3

The catalyst of Example 1 was studied using desorption and adsorptiontechniques to determine the pore size distribution, the average poreradius, the surface area and the total pore volume of the catalyst. Theresults of the studies are shown in Table 3.

Example 4

A catalyst was prepared in the manner of the catalyst prepared inExample 2 and having the same metal loadings as the catalyst prepared inExample 2 but having a 200 micron outer layer of alumina. The catalystwas studied using desorption and adsorption techniques to determine thepore radius size distribution, the average pore radius, the surface areaand the total pore volume of the catalyst. The results of the studiesare shown in Table 3.

TABLE 3 Catalyst Example 3 Example 4 Description 0.02% Pd/ 0.02%Pd/0.065% 0.038% Cu (100 Ag (200 micron micron layer) layer) BET SurfaceArea, m²/g 35 64 Tot. Pore vol., cc/g 0.12 0.22 Average pore radius, 7168 Angstrom Pore Radius Size Distribution, 10-250 10-250 Angstrom

The results shown in Table 3 demonstrate that the properties of thecatalyst are primarily determined by the layer, which can be relativelycarefully controlled and that the core contributes very little to thesurface area or pore volume. Thus the core primarily defines the bulkproperties of the catalyst (pressure drop, for example, as the bulkfluid mechanical properties are sensitive to the gross parameters of thecatalyst and not the fine details of layer thickness) and itscomposition is primarily important as to inertness to reaction whileshowing good bonding to the layer. Thus it is possible to relativelyindependently control both the bulk and microscopic properties of thecatalyst.

The adsorption and desorption profiles plotted against the pore radiusand the differential volume of the catalysts prepared in Examples 3 and4 are shown in the drawing.

1. A process for preparing a layered catalyst composition forselectively hydrogenating a C8-C19 diolefin to a C8-C19 monoolefin in ahydrocarbon mixture comprising the C8-C19 diolefin and the C8-C19monoolefin at selective hydrogenation conditions comprising a firstliquid phase, wherein the catalyst comprises: a. an inner corecomprising a first refractory inorganic component, b. an outer layerbonded to said inner core, the outer layer comprising a secondrefractory inorganic component having dispersed thereon at least oneIUPAC Group 10 metal and at least one IUPAC Group 11 metal, the processcomprising: i) coating an inner core with a slurry comprising the secondrefractory inorganic component, depositing on the coated core at leastone IUPAC Group 10 metal and at least one IUPAC Group 11 metal in thepresence of a second liquid phase, drying the coated core and calciningat a temperature of about 400 to about 900° C. for a time sufficient tobond the outer layer to the inner core and provide a layered support;and ii) reducing the product of step i) under reduction conditions toprovide the layered catalyst composition.
 2. The process of claim 1wherein the at least one IUPAC Group 10 metal and the at least one IUPACGroup 11 metal are dispersed on the second refractory inorganiccomponent by an impregnation step.
 3. The process of claim 1 wherein theslurry comprises an organic bonding agent.
 4. The process of claim 1wherein the second liquid phase comprises an aqueous solution of the atleast one IUPAC Group 10 metal.
 5. The process of claim 1 wherein thesecond liquid phase comprises an aqueous solution of the at least oneIUPAC Group 11 metal.
 6. The process of claim 1 wherein the firstrefractory inorganic component of the inner core is selected from thegroup consisting of alpha alumina, theta alumina, silicon carbide,metals, cordierite, zirconia, titania and mixtures thereof.
 7. Theprocess of claim 1 wherein the first refractory inorganic component ofthe inner core is cordierite.
 8. The process of claim 1 wherein thesecond refractory inorganic component of the outer layer is selectedfrom the group consisting of gamma alumina, delta alumina, eta alumina,theta alumina, silica/alumina, zeolites, nonzeolitic molecular sieves,titania, zirconia and mixtures thereof.
 9. The process of claim 1wherein the second refractory inorganic component of the outer layer isgamma alumina.
 10. The process of claim 1 wherein the at least one IUPACGroup 10 metal is a metal selected from the group consisting of platinumand palladium.
 11. The process of claim 1 wherein the at least one IUPACGroup 11 metal is a metal selected from the group consisting of copperand silver.
 12. The process of claim 1 further characterized in that theouter layer has a ratio of the at least one Group 10 metal to the atleast one Group 11 metal, and the ratio is substantially constant overthe outer layer.
 13. The process of claim 1 wherein the outer layerfurther comprises a modifier metal selected from the group consisting ofalkali metals, alkaline earth metals and mixtures thereof.
 14. Theprocess of claim 1 wherein the outer layer further comprises an alkalimetal selected from sodium or potassium and mixtures thereof.
 15. Theprocess of claim 1 wherein the outer layer has a thickness of about 50to about 300 microns.
 16. The process of claim 1 wherein the outer layerof the catalyst has a surface area of about 50-200 m2/g based on theweight of the outer layer.
 17. The product of the process of claim 1.18. The product of claim 17 wherein the catalyst has a concentration ofthe at least one IUPAC Group 10 metal of less than 0.1 wt-% based on theweight of the catalyst.
 19. The product of claim 18 wherein the catalysthas a concentration of the at least one IUPAC Group 11 metal of lessthan 0.2 wt-% based on the weight of the catalyst.